1. Field of the Invention
The invention relates to magnetrons and, more particularly, to filters for suppressing harmonic frequencies of the output frequency.
2. Description of the Prior Art
An electromagnetic energy generator widely used in the microwave field particularly in microwave ovens is the magnetron. Mutually perpendicular electric and magnetic fields extend within an interaction region defined between a central cathode and an anode member having a plurality of circumferentially disposed cavity resonators defined by vane members. Alternate resonators are coupled together by strapping between the vane members. The electric fields extend transverse to the axis of the anode member and the magnetic fields extend parallel to the anode axis. Electrons emitted from the heated cathode are accelerated toward the anode cavity resonators and rotate in a substantially circular orbital path to form a rotating spoke-like space charge. The electrons interact in energy-exchanging relationship with the electric fields in the cavity resonators to generate extremely high frequency energy oscillations.
The frequencies are in the microwave portion of the electromagnetic energy spectrum which is defined as having wavelengths in the order of from one meter to one millimeter and frequencies in excess of 300 MHz. The frequencies for microwave heating are regulated by the Federal Communications Commission with allotted frequencies at 915 .+-. 13 MHz and 2450 .+-. 50 MHz. The energy is coupled from the magnetron by means of output members comprising antenna probes having one end secured to an anode member vane member. The output antenna member is housed within a dielectric dome which is part of the overall evacuated tube envelope.
During operation of microwave heating apparatus the problem with the generation of harmonic frequencies is a continuing one which must be handled. Presently, waveguide filters as well as door seal suppression structures are utilized to attenuate these spurious output signals. The need continues, however, for new and improved means for suppression of the undesired harmonic frequencies of the fundamental frequency generated by a magnetron.